Heightened avalanche conditions exist on slopes steeper than 35. Large and destructive Glide avalanches and cornice falls are possible where rain has saturated old snow. Avoid terrain with open cracks in the snow and overhung cornices near ridge lines.

Issued: 7:11 PM PST Sunday, February 4, 2018

by Dennis D'Amico

Elevation

Monday

Outlook

The Day 2 avalanche danger outlook is different than the Day 1 avalanche danger
forecast. The Day 2 avalanche danger outlook has a higher level of uncertainty in
the regional avalanche danger but can still show the expected danger level trend
versus the Day 1 forecast. Also, the Day 2 avalanche outlook does not have avalanche
problems defined as a result of the increased uncertainty.

Outlook for Tuesdayi

Above Treelinei

Above Treeline

Above Treeline is the highest of the three elevation bands used in NWAC
forecasts. It includes alpine areas where the most snow falls and the winds
are the strongest. Above Treeline is not an exact elevation, but a
characteristic of the terrain, beginning as the treeline transitions into
open slopes extending to ridges and to the tops of the ridges or
non-volcanic peaks and to the cascade crest level on the Cascade volcanoes.
Due to the lack of high alpine snowpack data available to the forecasters,
the upper limit roughly corresponds to a 7-8,000 level.

Outlook for Tuesdayi

Moderate

Near Treelinei

Near Treeline

Near Treeline is the middle of the three elevation bands used in NWAC
forecasts. It is a transition zone between dense forests and treeless alpine
areas. It is the narrowest of the three elevation bands, extending only a
few hundred feet above and below the treeline. It varies locally, and is not
a constant elevation or width.

Monday

Moderate

Outlook for Tuesdayi

Low

Generally safe, watch for unstable snow on isolated terrain features.

Below Treelinei

Below Treeline

Below Treeline is the lowest of three elevation bands used in NWAC forecasts.
It extends from valley floors, or snowline, to Near Treeline. Open areas and
sparse trees are possible. Snowfall tends to be less than the other
elevation bands. Tree cover shelters the snow from wind effects.

Monday

Moderate

Outlook for Tuesdayi

Low

Generally safe, watch for unstable snow on isolated terrain features.

Danger Scalei

Danger Scale

The North American Avalanche Danger Scale is a five level scale used to communicate the
danger of avalanche to backcountry recreationalists. The danger is a combination of the
expected likelihood, size, and distribution of avalanches. It provides a very basic
description of the avalanche conditions.

No Rating

Low

Moderate

Considerable

High

Extreme

Issued: 7:11 PM PST Sunday, February 4, 2018

by Dennis D'Amico

Avalanche Problems for Monday

Avalanche Problems

Avalanche Problems are categories of avalanche activity. The Problems may not describe
all avalanche activity you might observe, but they categorize the avalanches by how we
manage the risk in the terrain. This approach focuses on relevant observations you can
make in the field and how to treat the avalanche risk.

The forecasts list up to three current Problems, along with the spatial distribution, the
likelihood of avalanches, and anticipated size. Forecasters may provide specific details
to a Problem in the forecast discussion tab.

This link has detailed descriptions of
each Avalanche Problem and suggestions for risk treatment.

Glidei

Glide avalanches occur when water lubricates the interface between the snowpack and the ground. These avalanches are difficult to predict and best managed by avoiding terrain below glide cracks.

Glide

A release of the entire snow cover as a result of gliding over the ground. Glide avalanches can be composed of wet, moist, or almost entirely dry snow. They typically occur in very specific paths, where the slope is steep enough and the ground surface is relatively smooth. They are often preceded by full depth cracks (glide cracks), though the time between the appearance of a crack and an avalanche can vary between seconds and months. Glide avalanches are unlikely to be triggered by a person, are nearly impossible to forecast, and thus pose a hazard that is extremely difficult to manage.

Predicting the release of Glide avalanches is very challenging. Because Glide avalanches only occur on very specific slopes, safe travel relies on identifying and avoiding those slopes. Glide cracks are a significant indicator, as are recent Glide avalanches.

This Glide avalanche broke to the ground on a smooth, grassy slope. From all the mud on the bed surface, water pooling at the base of the snowpack likely caused the failure.

Avalanche Problemi

Aspect/Elevationi

Likelihoodi

Sizei

Loose Weti

Loose wet avalanches occur where water is running through the snowpack, and release at or below the trigger point. Avoid terrain traps such as cliffs, gullies, or tree wells. Exit avalanche terrain when you see pinwheels, roller balls, a slushy surface, or during rain-on-snow events.

Loose Wet

Release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. They generally move slowly, but can contain enough mass to cause significant damage to trees, cars or buildings. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.

Travel when the snow surface is colder and stronger. Plan your trips to avoid crossing on or under very steep slopes in the afternoon. Move to colder, shadier slopes once the snow surface turns slushly. Avoid steep, sunlit slopes above terrain traps, cliffs areas and long sustained steep pitches.

Several loose wet avalanches, and lots of pinwheels and roller balls.

Avalanche Problemi

Aspect/Elevationi

Likelihoodi

Sizei

Aspect/Elevation

The Aspect/Elevation diagram describes the spatial pattern of the Avalanche Problem by aspect (the
direction a slope faces) and elevation band (Above, Near, or Below Treeline). The diagram will be
filled with black where the Avalanche Problem may exist. You can view the diagram as you would a
mountain on a topographic map. The outer ring represents the Below Treeline elevation band, middle
ring Near Treeline, and the inner ring Above Treeline. The diagram is oriented like a compass, with
the top wedges representing north aspects, the left wedges representing west, etc.

Likelihood

Likelihood is a description of the chance of encountering a particular Avalanche Problem. It combines
the spatial distribution of the Problem and the sensitivity or ease of triggering an avalanche. The
spatial distribution indicates how likely you are to encounter the Problem in the highlighted
avalanche terrain. The sensitivity indicates how easy it is to trigger avalanches including both
natural and human triggered avalanches.

Size

Size is based on the destructive potential of avalanches.

SMALL avalanches are relatively harmless to people unless they push you into a terrain trap.

LARGE avalanches could bury, injure or kill a person.

VERY LARGE avalanches could bury cars, destroy a house, or break trees.

HISTORIC avalanches are even more destructive, and nearing the maximum size the slope could
produce.

Recent images from NWAC:

Avalanche Summary:

Wet weather over the weekend created moist to wet surface snow conditions up to 6500 feet. A natural Loose Wet avalanche cycle occurred Friday and Saturday. Observers reported both natural cornice falls and glide avalanches. We’ve received minimal reports of Wet Slab avalanches. Poor visibility and stormy conditions have limited observations at higher elevations. Across the region rain totals averaged 1” during daylight hours on Sunday with 1.06” at Steven’s Pass, .95” at Snoqualmie Pass, and .88” at Paradise on Mt Rainier.

Observations

Stevens Pass

NWAC Avalanche Forecasters and observers noted numerous natural wet loose avalanches on all aspects Friday and Saturday. These avalanches ranged from small to large, with some travelling 1000 vertical feet.

Snoqualmie Pass

On Sunday NWAC observer, Matt Schonwald, found a saturated snowpack with rain water more than 2 feet below the snow surface. Alpental Ski Patrol reported audible cornices collapses along ridges in the Alpental Valley on Saturday. Both patrol and NWAC observers reported Glide avalanches, visible glide cracks, and many wet loose avalanches

Forecast for Monday:

While avalanches will be difficult to trigger today, they could have serious consequences. Glide Avalanches and cornice falls could be big enough to bury or kill you. Both of these types of avalanches form in specific types of terrain. The best way to stay safe is to avoid areas where these avalanches form and release. Watch out for slopes with visible glide cracks or where known rock slabs lie under the snowpack. Give yourself an extra wide margin of safety near ridges that could hold cornices, and avoid slopes with cornices overhead.

Many Loose Wet avalanches ran in the past couple days. This avalanche cycle is tapering off but is still possible today. While these avalanches may be the smallest and most predictable of today’s avalanche flavors, they could still be big enough to injure you. Avoid traveling through or above terrain that could increase the consequences of being caught in an avalanches such as or cliffs, gullies, or rocky slopes.

Avalanche Summary:

Wet weather over the weekend created moist to wet surface snow conditions up to 6500 feet. A natural Loose Wet avalanche cycle occurred Friday and Saturday. Observers reported both natural cornice falls and glide avalanches. We’ve received minimal reports of Wet Slab avalanches. Poor visibility and stormy conditions have limited observations at higher elevations. Across the region rain totals averaged 1” during daylight hours on Sunday with 1.06” at Steven’s Pass, .95” at Snoqualmie Pass, and .88” at Paradise on Mt Rainier.

Observations

Stevens Pass

NWAC Avalanche Forecasters and observers noted numerous natural wet loose avalanches on all aspects Friday and Saturday. These avalanches ranged from small to large, with some travelling 1000 vertical feet.

Snoqualmie Pass

On Sunday NWAC observer, Matt Schonwald, found a saturated snowpack with rain water more than 2 feet below the snow surface. Alpental Ski Patrol reported audible cornices collapses along ridges in the Alpental Valley on Saturday. Both patrol and NWAC observers reported Glide avalanches, visible glide cracks, and many wet loose avalanches

Forecast for Monday:

While avalanches will be difficult to trigger today, they could have serious consequences. Glide Avalanches and cornice falls could be big enough to bury or kill you. Both of these types of avalanches form in specific types of terrain. The best way to stay safe is to avoid areas where these avalanches form and release. Watch out for slopes with visible glide cracks or where known rock slabs lie under the snowpack. Give yourself an extra wide margin of safety near ridges that could hold cornices, and avoid slopes with cornices overhead.

Many Loose Wet avalanches ran in the past couple days. This avalanche cycle is tapering off but is still possible today. While these avalanches may be the smallest and most predictable of today’s avalanche flavors, they could still be big enough to injure you. Avoid traveling through or above terrain that could increase the consequences of being caught in an avalanches such as or cliffs, gullies, or rocky slopes.

USE AT YOUR OWN RISK

This Backcountry Avalanche Forecast is provided in conjunction with the US Forest Service, and is intended for personal and recreational purposes only. Safe backcountry travel requires preparation and planning, and this information may be used for planning purposes but does not provide all the information necessary for backcountry travel. Advanced avalanche education is strongly encouraged.

The user acknowledges that it is impossible to accurately predict natural events such as avalanches in every instance, and the accuracy or reliability of the data provided here is not guaranteed in any way. This forecast describes general avalanche conditions and local variations will always occur. This forecast expires 24 hours after the posted time unless noted otherwise.